Start with the seven basic ratings covering all forms of television content: TV-Y (acceptable for all children), TV-Y7 (acceptable for children 7 or older), TV-Y7 (FV) (acceptable for children 7 or older, but with scenes of fantasy violence), TV-G (acceptable for general audiences), TV-PG (parental guidance suggested), TV-14 (parents strongly cautioned against letting children view it) and TV-MA (intended for adult audiences). These provide a good general overview of the content.
Focus on the three ratings with the "Y" in them. All such programs are designed specifically for children, but the distinction between them may be a little vague. TV-Y is designed for very young children, with extremely mild themes and a gentle tone. "Sesame Street" is a good example of such programming. TV-Y7 is still meant for young people, but may be more sophisticated or intense, making it more appropriate for kids in grade school. "Spongebob Squarepants" is a good example of such programming. Finally, TV-Y7 (FV) is still acceptable for grade school kids, but may contain images of fantasy violence which some parents may object to. A "Batman" cartoon with the hero punching the bad guy is a good example of such programming.
Examine the remaining four ratings on the list. They follow the same basic pattern as movie ratings. A TV-G program isn't specifically meant for children, but is safe for family viewing. A nature documentary is a good example of such programming. TV-PG is a little more intense and may contain adult situations. Many situation comedies fall into this realm. TV-14 contains a fair amount of adult content and parents should carefully consider whether pre-teens should watch it. Many cop shows on network TV fall into this realm. Finally, TV-MA is intended exclusively for adult audiences, the same way a movie rated "R" or "NC-17" would be. It includes a lot of evening cable shows such as "The Sopranos."
Look for the little letters below the main rating itself. These letters appear on the three most extreme ratings (TV-PG, TV-14 and TV-MA) and are intended to provide a specific rundown of the kinds of content on the show. Some parents, for example, may not object to coarse language for an older child, but may balk at sexual situations. Those little letters are intended to help clarify such distinctions. "D" stands for suggestive dialogue (usually allusions to sex). "L" means coarse or crude language such as swear words. "S" means overt sexual content and "V" means violence.